JavaScript Frameworks - Beginning JavaScript - page 568

options that the object uses when making a request. The options object can contain a variety of option
properties to alter the behavior of Ajax.Request(); the following table describes just a few of them.

Option Description

asynchronous Determines whether the XMLHttpRequest object makes the request in asyn-

chronous mode or not. The default is true .

method The HTTP method used for the request. The default is “post” . “get” is

another valid value.

onSuccess A callback function invoked when the request completes successfully.

onFailure A callback function invoked when the request completes, but results in an

error status code.

parameters Either a string containing the parameters to send with the request, or an

object containing the parameters and their values.

For a complete list of options, visit the Prototype documentation at http://www.prototypejs.org/
api/ajax/options .

All callback functions are executed and passed a parameter containing the XMLHttpRequest object
used to make the request. Making a request with Prototype looks something like the following code:

function request_onsuccess(request)
{
alert(request.responseText);
}

function request_onfailure(request)
{
alert(“An error occurred! HTTP status code is “ + request.status);
}

var options = new Object();
options.method = “get”;
options.onSuccess = request_onsuccess;
options.onFailure = request_onfailure;

new Ajax.Request(“someTextFile.txt”, options);

The fi rst few lines of code defi ne the request_onsuccess() and request_onfailure() functions.
These functions all accept one parameter called request. The value of this parameter will be the
XMLHttpRequest object used to make the request.

Prototype actually passes an Ajax.Response object to all Ajax request callbacks. It is very similar
to the XMLHttpRequest object and adds extra functionality. To access the XMLHttpRequest object
directly, use the transport property; for example, request.transport . After the function defi ni-
tion, you create an options object The fi rst option you set is the method option, which you set to get .
The next option is the onSuccess option, and you assign the request_onsuccess() function to
this option. The fi nal option is onFailure , which you assign the request_onfailure() function.